1. Field
Embodiments of the present invention relate to a vehicle braking system and a control method thereof which secure braking stability of a vehicle.
2. Description of the Related Art
Recently, hybrid vehicles and electric vehicles are provided with an internal combustion engine and a motor which is driven by electric energy of a high voltage battery, and are thus new-generation environmental vehicles driven by such a motor.
The high voltage battery to supply driving power to the motor is mounted in the hybrid vehicles and electric vehicles. Such a high voltage battery supplies electric energy to the motor during driving of the motor and charges electric energy generated by the motor during regenerative braking or driving of the engine.
In more detail, the motor performs the function of an electric generator if a driver gives a decelerating command or a braking command, and thus generates electric energy. At this time, the battery performs charging. While the motor acts as the generator in this manner, braking torque is generated on wheels, and such braking torque is referred to as regenerative braking force.
In order to secure braking force required by a driver during braking, the hybrid vehicles and electric vehicles use regenerative braking force using the motor of the vehicle and hydraulic braking force using brake hydraulic pressure. Here, the hydraulic braking force is a value obtained by subtracting regenerative braking force generated by the motor from required braking force.
Further, the hybrid vehicles and electric vehicles stop regenerative braking and controls hydraulic braking force using brake hydraulic pressure, when a safety function, such as an ABS or an ESC, is operated during regenerative braking, thereby securing braking stability of the vehicle.
Here, the hybrid vehicles and electric vehicles pass through a conversion section between regenerative braking and hydraulic braking, and may obstruct braking stability of the vehicle due to maintenance or increase of slippage of drive wheels by remaining regenerative braking force in the switch section in which regenerative braking is not stopped.
Further, in the hybrid vehicles and electric vehicles, rapid change of brake hydraulic pressure due to operation of the safety function, such as the ABS or the ESC, in the switch section between regenerative braking and hydraulic braking provides undesirable fluctuation to the motor which is not stopped according to the remaining amount of regenerative braking force, and may thus obstruct braking stability of the vehicle.